In U.S. application Ser. No. 383,921, filed July 30, 1973 and now U.S. Pat. No. 3,996,283, there is described a process for the preparation of multinuclear aromatic polyamines by the condensation of aromatic amines with formaldehyde in the presence of water and acid catalysts In that process, the aqueous condensation mixture obtained after the reaction has been completed is extracted with a hydrophobic solvent. The resulting solvent phase is then worked-up to recover the desired polyamine, while the aqueous phase, which contains the acid catalyst in the form of amine salts, is returned to the beginning of the process with the addition of fresh amine as starting material.
The above-mentioned process marked a major improvement over the previously known process of aniline/formaldehyde condensation carried out with acid catalysts, particularly since it obviated the need for neutralization of the acid catalyst. As a result of this, the effluent water from the process is substantially free from salt and the corresponding consumption of acid catalyst and alkalizing agent is virtually zero. This process, however, has some disadvantages. Thus, the circulation of the aqueous catalyst includes varying quantities of water added from outside (depending on the quantity of formaldehyde which is introduced in the form of aqueous solutions and depending on the quantity of the water produced in the condensation reaction) and this additional water must be removed from circulation, generally by distillation.
It is therefore, an object of the present invention to improve the above process with a view towards keeping the quantity of water in the circulation of aqueous catalyst constant. In other words, the purpose of the instant invention is to relieve the circulation of additional water introduced from outside or formed chemically and at the same time to enable the water introduced and formed in the reaction to be removed by a simple water separator. From a processing point of view, the quantitative removal of the varying quantities of water added in the course of the reaction from the aqueous catalyst would significantly increase the flexibility of the system since the catalyst circulation could be kept constant even with varying outputs and with varying aniline/formaldehyde ratios and hence with varying quantities of water introduced into the process. It would therefore be possible to produce various types of polyamine always under optimum conditions. The elimination of the distillation step to remove the water introduced and formed in the course of the reaction would further simplify and improve the prior process.